System and method for validation of hearing aids for infants using a speech signal

ABSTRACT

A system for validation of a hearing aid performance, especially in small children is disclosed. The validation of the performance of hearing aids after having being fitted to a small child who is not able to subjectively provide responses to sounds presented to the child via the hearing aids, is instead done in an objective manner, by using a naturally occurring signal, which has been modulated in order to create an ASSR evoking speech stimulus which is not considered as noise by a hearing aid.

This application is a Continuation of copending application Ser. No.17/699,848, filed Mar. 21, 2022, which is Continuation of applicationSer. No. 16/457,364, filed on Jun. 28, 2019 (now U.S. Pat. No.11,310,612 issued Apr. 19, 2022), which claims priority under 35 U.S.C.§ 119(a) to application Ser. No. 18/180,836.1, filed in Europe on Jun.29, 2018, all of which are hereby expressly incorporated by referenceinto the present application.

FIELD

The present disclosure relates to a hearing diagnostic system, which isconfigured to perform an objective validation of a hearing aidperformance by sound presentation to the ear of a test person when noactive intentional responses can be obtained from the person under test.More specifically, the disclosures relate to a system comprisingdiagnostic devices, and methods which by a measure of auditory evokedresponses from the scalp of a person enables a validation of the hearingaid performance in especially infants and young children.

BACKGROUND

When a child is diagnosed with a potential hearing loss from a hearingscreening performed in an early stage after birth, the child is referredto further diagnostic testing to evaluate the cause of the hearing lossand the degree of the hearing loss present. Especially the degree of ahearing loss is important to evaluate, and tests have been developed toindicate the degree of hearing loss from a measure of neurologicalactivity caused by hearing. One challenge is, that a small child, —be itnormally hearing or one who has degraded or loss of hearing—cannotphysically provide an answer as to whether he or she is able to hear asound or not, and therefore an objective neurological test is performedinstead. Such tests include among other tests measures of the brainactivity related to hearing which are called evoked potentials, such asauditory brain responses (ABR) or auditory steady state responses(ASSR). In such tests, a stimulus designed to generate an auditoryevoked response from the brain is transmitted into the ear of a child,and electrodes arranged on the scalp of the child record any brainresponse arising from the stimulus. From these responses, provided atdifferent frequencies of hearing, the amount of hearing loss for eachfrequency can be assessed in an audiogram and a hearing aid may beprogrammed to compensate for the measured hearing loss indicated by theaudiogram data.

Other types of stimuli signals used for similar testing is the CorticalAuditory Evoked potential (CAEP) test. These signals are configured asseveral different speech sounds called phonemes, like ‘m’, ‘g’ and ‘t’,which are presented through a loudspeaker at a range of levels. Evokedresponses to the sounds are recorded from the surface of the headrecorded via electrodes and analyzed on a computer. Thus, the CAEP testsignals are merely signals including only phonemes, and is notconfigured as running speech. In more detail, a phonemes is short pieceof speech, which in CAEP measurements are used as stimulus.

Upon having programmed the hearing aid to compensate for a measuredhearing loss, the compensation provided by the hearing aid has to beverified and further validated to ensure that the hearing loss iscorrectly compensated for and that the child can actually hear relevantsounds played through the hearing aid. The verification process aims atproviding an objective estimate of the sound that the hearing aid isproducing in the ear of a person. This process is to ensure that thehearing aid is performing as intended and programmed. However, when ithas been ensured that the hearing aid is performing as intended (e.g.meets the prescribed target gain etc.), it is subsequently necessary toperform a more subjective evaluation of whether the hearing aidperformance actually also meets the needs of the hearing impairedperson. This procedure is called validation. Traditionally, in thisvalidation process the hearing impaired person actively has to providean oral or other physical response to evaluate if a certain sound, levelof sound, noise, etc. is meeting the needs for the hearing impaired(i.e. a “subjective evaluation”). Thus, when fitting children,especially infants or very small children these physical responses orreactions to a sound played into the ear of the child cannot beevaluated sufficiently, since the child might not be able to speak orarticulate intentionally in response to the sounds played to the child.Accordingly, the effectiveness of the amplification settings should beevaluated by other means. For children, current methods rely on theunderstanding and active participation from the child, which cannot begranted considering younger children or infants.

Therefore, there is a need to provide for a system, method and tool,which enables an evaluation and validation of the “subjective” hearingperformance of a hearing aid, when no subjective physical, oral, oractive intentional response can be obtained from the test person, e.g. asmall child with a hearing loss.

SUMMARY

The current disclosure provides a system, method, and tool which enablese.g. a hearing care professional to objectively validate the hearing aidperformance for a child, when no active intentional responses can beexpected from the child who is being treated for a hearing loss. Thesystem is configured to perform a hearing test, wherein a validationmode is used to evaluate the hearing ability of a person, e.g. a smallchild, in the aided condition (i.e. when the child is wearing a hearingaid). In order to perform such objective evaluation, the systemcomprises one or more electrodes, which are configured to be arranged onthe scalp of a person under test, and where the one or more electrodesare configured to be connected to a diagnostic device. It should benoted that the “person under test”, the “hearing impaired” or othersimilar denotation of the test person in this context is mainly relatedto a small child, who is unable to provide an intentional physicalresponse to a stimulus signal. However, it could also include otherhearing impaired persons, who have difficulties in expressing themselvesphysically or orally. Similarly, “hearing aid” should be understood tobe any hearing prosthetic device, including cochlear implants,bone-anchored hearing devices etc.

In order to generate a stimulus signal used in the objective validationmode, the system furthermore comprises a sound emitting device, which isconfigured to be connected to the diagnostic device and to transmit agenerated sound stimulus to the aided ear of a person. Furthermore, thediagnostic device is configured to be set in at least a validation mode,and for transmitting a sound stimulus, recording and processing theresponse data received from the hearing test, the diagnostic toolcomprises; a signal generator configured to transmit a generatedstimulus to the sound emitting device; a recording processor configuredto receive a response signal from the one or more electrodes arranged onthe scalp of the person under test; and a control unit configured tocontrol the mode of operation of the diagnostic device, wherein in thevalidation mode of operation, the signal generator is configured togenerate the sound stimulus and to transmit the generated sound stimulusto the sound emitting device, wherein the generated sound stimulus isconfigured as an amplitude and/or frequency modulated naturallyoccurring sound.

In other words, a system including a diagnostic device and one or moreelectrodes configured to record an auditory evoked response from thebrain of a person is provided for. The diagnostic device is configuredto transmit a stimulus, which is generated from a naturally occurringsound. The naturally occurring sound is either input to the diagnostictool or is already provided in a sound processor of the diagnostic tool,and the naturally occurring sound is amplitude and/or frequencymodulated so as to create a frequency and/or amplitude modulatedstimulus from a naturally occurring sound. By using such amplitudeand/or frequency modulated naturally occurring sound it is possible tocreate a sound stimulus which is able to evoke auditory brain responses,while at the same time being not only “speech-like” but actually createdfrom, e.g., a speech signal, and which thus is less distorted than theknown types of speech-like stimuli that are used for detecting auditoryevoked responses.

Accordingly, the definition of natural occurring sound should beconstrued as a sound existing naturally in the environment of humans,and which has not been processed by any machine, computer, processor orsimilar. In accordance herewith, natural means “existing in or formed bynature (as opposed to artificial)”. Accordingly, the natural occurringsound could be a speech signal as spoken by a human person, birdssinging, dogs barking, children playing, live music, piano music etc. Inother words, the natural occurring sound is in case of speech to beconstrued as “running-speech”, which is defined as the continuous soundof spoken dialogue from which the listener is able to distinguishindividual words and sentences. Thus, the stimulus used in this setup isa preferred embodiment, a natural occurring sound, such as runningspeech, which is frequency and/or amplitude modulated. This stimulus isin contrast to e.g. CAEP (which are pieces of speech used as stimulus asprevious explained), a stimulus containing running speech, and not onlyselected pieces (phonemes) of running speech.

It should be noted that in a preferred embodiment, the auditory evokedresponses that are detected are auditory steady state responses (ASSR)or envelope-following responses (EFR).

In more detail, when the validation of the “subjective” performance of ahearing aid is assessed and no subjective physical, oral, or activeintentional response can be obtained from the test person, e.g. a smallchild with a hearing loss, it is important that the test stimulus issufficiently speech-like to be classified as speech by one or morehearing aids arranged behind the ears of the child. It should be notedthat the applications described herein could similarly be used forin-the-ear type hearing aids. Regularly used auditory evoked-responsestimuli are, when presented to the hearing aid, processed as noise bythe hearing aid, and can therefore potentially lead to misleadingresults of the validation process. Instead, according to the disclosure,it has been found that providing a naturally occurring sound, such asspeech, and generating a frequency and/or amplitude modulated version ofthis naturally occurring sound, an auditory evoked-response stimuluswhich is not considered as noise by the hearing aid can be generated.Thus, in the validation process of a hearing aid, such a stimulus ispresented to the hearing aid, and comprises components of the stimulussignal which are not modified or removed from the stimulus by thehearing aid, which would have been the case for e.g. a standard chirpstimulus. Thus, by providing a frequency and/or amplitude modulatedstimulus based on a naturally occurring signal, e.g. speech, in thevalidation step of the hearing aid test, it is possible to get anauditory evoked response from the brain of the test person, so as toobjectively and correctly, in terms of hearing-aid gain and selection ofsignal-processing features, evaluate the “subjective” performance of thehearing aid.

It should be noted that in the following, the generated sound stimulusshould be understood as being a sound stimulus which is purely based ona naturally occurring sound (refer to previous definition), preferably aspeech signal, which has been amplitude and/or frequency modulated tocreate the necessary auditory evoking components in the signal.

For transmitting the generated stimulus based on a naturally occurringsound to the hearing aids, the sound emitting device may in anembodiment be configured as the one or more hearing aids, which arearranged on the ear or ears of the test person in the validation mode ofthe diagnostic device. Thus, in an embodiment the generated soundstimulus may be transmitted into the ear of a hearing-aid user directlyvia the hearing aids.

In a more preferred embodiment, the sound emitting device is configuredas a loudspeaker. The loudspeaker is in this embodiment connected to thediagnostic device and is externally arranged in relation to the one ormore hearing aids. By externally arranged should be construed that theloudspeaker is located in the ambient surrounds to the hearing aids.That is, the loudspeaker in this embodiment may be arranged in the “testroom” at a distance away from the hearing aids arranged on thepatient/child. The loudspeaker is configured to receive the generatedsound stimulus from the signal generator and to play the generated soundstimuli to the one or more hearing aids arranged of the ears of aperson. By presenting the sound stimulus to the hearing aid via aloudspeaker, it is ensured that the sound presented to the ear of theuser is processed in the hearing aid in a regular way. Thus, the soundis presented to the ear of a user with the same hearing aid processingas used in daily life with real speech signals, and due to the fact thatthe sound stimulus is generated from a naturally occurring sound, thesound is not considered as noise by the hearing aid, and thereforetransmitted substantially with all of the frequency content to the earof a user and with the amplification adequate for real speech. Theamplitude and/or frequency modulations applied to the naturallyoccurring sound then acts to evoke auditory brain responses, which maybe recorded by the electrodes arranged on the scalp of the hearing-aiduser.

The fact that the proposed stimulus is not only speech-like, butactually based on a naturally occurring signal, e.g. speech, has theadditional advantage to underpin the face validity of the validationtest towards both clinicians and the parents/caregivers of the childunder test. Thus, in the validation mode, the diagnostic tool isconfigured to transmit the generated sound stimulus to the one or morehearing aids via the hearing aids or via the externally arrangedloudspeaker, whereby the hearing aids presents the transmitted generatedsound stimulus in the ear of the person, such that auditory evokedresponses are generated and recorded by the electrodes arranged on thescalp. The recorded evoked responses are transmitted to the diagnosticdevice as auditory evoked responses (AER), such as auditory steady stateresponses (ASSR).

The naturally occurring sound which is processed with an amplitudeand/or frequency modulation is preferably a sound recorded in the testenvironment of the child being tested. That is, in an embodiment, thesound stimulus is generated from a recording of the naturally occurringsound, which is input to the diagnostic device. That is, for example, aparent to a child may speak into an external microphone, whereby thespeech of the parent is recorded and used as input to the sound stimulusgeneration. Thus, the naturally occurring sound is in an embodimentprovided as speech from a human person, and the recorded naturallyoccurring sound is transmitted wired or wirelessly to the diagnosticdevice. In the diagnostic device, the sound stimulus generator processesthe recorded human speech to generate an amplitude and/or frequencymodulation of the recorded naturally occurring sound resulting in thesound stimulus which is transmitted to loudspeaker or directly to thehearing aids of the child under test, as described above. By enablingthe possibility of recording speech from e.g. a parent, it is ensuredthat the child, that is being tested for a hearing loss and fitted witha hearing aid, is presented with the voice of e.g. the mother or fatherof the child, instead of a synthetically generated voice signal, whichmay be constructed from e.g. a plurality of different speakers' voices(e.g. the international speech test signal, (ISTS)). The ISTS signal isan internationally recognized test signal that may be used in thetechnical evaluation of hearing instruments, and for probe-microphonemeasurements. The ISTS is based on natural recordings of speech which isnon-intelligible due to remixing and segmentation. Instead the voicesthat the child are presented with are as close to their normal dailylife as possible, and at the same time the mother or father of the childcan actually experience how their child is able to hear their voicesduring the validation test, and as the direct result of the hearing-aidfitting.

In another embodiment, the naturally occurring sound may be recorded viaa computer or another external device and subsequently transmitted tothe diagnostic tool. That is, the sound stimulus generation of therecorded naturally occurring sound, preferably a speech signal, may beperformed in the diagnostic tool, but may also be performed in a deviceexternal to the diagnostic tool, such as in a computer, an app on amobile phone or similar devices. Thus, independently of the medium onwhich the sound stimulus generation (processing of the recorded sound)takes place, the processing steps performed on the recorded naturallyoccurring signal are the same.

Thus, in an embodiment, the recorded naturally occurring sound isreceived in a sound signal generator (e.g. in the diagnostic tool oranother medium capable of processing a signal), wherein the recordednaturally occurring sound is processed in the following steps; first therecorded naturally occurring sound is filtered into a plurality offrequency sub-bands; secondly, each of the plurality of frequencysub-bands are independently amplitude and/or frequency modulated;wherein in a third step the amplitude and/or frequency modulatedsub-bands are combined to form the sound stimulus. Thus, the naturalrecorded sound, preferably a speech signal, is split into differentfrequency sub-bands to ensure that multiple narrower ranges of theentire frequency-range of hearing can be tested simultaneously by meansof the sound stimulus. Thus, each of the bands are frequency and/oramplitude modulated to ensure that each of the sub-bands comprisescomponents which are able to stimulate an auditory evoked response,preferably an auditory steady state response (ASSR).

In an alternatively preferred embodiment, the recorded naturallyoccurring sound is received in a sound signal generator (e.g. in thediagnostic tool or another medium capable of processing a signal),wherein the recorded naturally occurring sound is processed in thefollowing steps; first the recorded naturally occurring sound isfrequency or amplitude modulated with a plurality of modulator functionshaving different modulation rates;

-   -   secondly each of the plurality of amplitude and/or frequency        modulated recorded naturally occurring sounds is subsequently        filtered by one of a plurality of frequency sub-bands chosen for        each of the modulations of the recorded naturally occurring        sound;    -   wherein further the amplitude and/or frequency modulated        sub-bands are combined to form said sound stimulus.

In more detail for each of the alternatives described above, theamplitude and/or frequency modulated frequency sub-bands may be adjustedin magnitude to align with a predetermined set of values. This is toensure that the magnitude of the sub-bands is either in accordance witha desired test target level for each stimulus sub-band in question, orto ensure that the generated stimulus resembles a natural speech signal.The latter approach serves two purposes: 1) to further ensure that thehearing aid will process the stimulus as speech and not as noise, and 2)to ensure that the validation test actually is indicative of whether ornot a real speech signal is audible when the hearing aid is used.

Accordingly, in an embodiment, the predetermined set of values isprovided as a set of band powers of a standardized speech test signal atany of the frequency sub-bands or the predetermined set of values isprovided as band powers of the recorded naturally occurring sound. Itshould be construed that the standardized speech test signal in anembodiment may be the international speech test signal (ISTS), or e.g.the ICRA 1-talker babble (ref. Wouter A. Dreschler, Hans Verschuure,Carl Ludvigsen & Søren Westermann (2001) ICRA Noises: Artificial NoiseSignals with Speech-like Spectral and Temporal Properties for HearingInstrument Assessment: Ruidos ICRA: Señates de ruido artificial conespectro similar al habla y propiedades temporales para pruebas deinstrumentos auditivos, Audiology, 40:3, 148-157, DOI:10.3109/00206090109073110). In this way, it may be ensured that thesound stimulus generated from the naturally occurring sound has adequatemagnitude to resemble a normal speech signal, so as to cause an auditoryevoked response representative of real speech input, while at the sametime ensuring that the hearing aids will process the entire stimulussignal as speech and not as noise.

In any of the embodiments described above it should be noted that also astandardized speech signal can be used as the input signal to the signalgenerator.

Due to the frequency and/or amplitude modulation of the naturallyoccurring sound, being the recorded sound or e.g. the standardizedspeech signal, the signal may be somewhat distorted in comparison to aclean speech signal. However, to improve the speech content of theresulting stimulus, the processing step of generating the sound stimulusmay include a further step of setting an amplitude and/or a frequencymodulation factor for one or more of the plurality of sub-bands to 0, soas to leave the respective sub-band unmodified. This in effect ensuresthat the frequency and/or amplitude modulation does not affect thespecific sub-band of which the speech content in full will be leftunmodified. This can be advantageous for enforcing the point that thestimulus is (very close to) real speech, which is a potentiallyimportant trait of the proposed validation method in terms of thecounselling of the parents/caregivers of the child under test, as wellas the clinician administering the validation test.

The system is configured such that the auditory evoked responses,preferably auditory steady state responses, can be detected frommeasurements by the electrodes arranged on the scalp of the test person,preferably a small child. The system is thus configured such that thediagnostic tool in the validation mode controls the transmission of thesound stimulus to the ears of the child via the hearing aids. Thestimulus signal is transmitted continuously until a response is measuredfor all of the sub-band frequencies tested, or until the test isterminated on the grounds of futility (i.e. detection not expected evenwith prolonged testing). Accordingly, in an embodiment, the diagnostictool is configured to control a first transmission, wherein the entirefrequency band of the sound stimulus is played to the hearing aids. Upondetecting a response from the electrodes within a specified frequencysub-band, the specific frequency sub-band is turned off (i.e. set to 0)so as to remove the specific frequency sub-band for which a response isdetected from the stimulus. This is done to minimize stimulus bandinteraction, or spread of excitation in the cochlea, that may hamperdetection of the yet undetected frequency sub-bands. Thus, the remainingsub-band evoked responses may be detected faster. Thus, for every time aresponse from the electrodes is detected for a specified frequency, therespective sub-band accounting for this frequency is turned off, and theremaining frequency content of the stimulus signal is presented to theears of the small child via the hearing aids.

In principle any frequency could be tested for in the described setup.However, the frequencies that are most interesting for characterizinghearing losses are the main focus of this application. Thus, in anembodiment, the naturally occurring sound may be band-pass filtered intofour one-octave wide frequency sub-bands having center frequencies of500 Hz, 1 kHz, 2 kHz, and 4 kHz.

Preferably each of the sub-bands may be amplitude and/or frequencymodulated with modulator functions having different modulation rates foreach of the sub-bands. This allows the auditory evoked responses fromthe respective stimulation sub-bands to be separated in the frequencydomain.

In general, and as described in more detail herein, each of themodulator functions applied to generate the sound stimulus from thenaturally occurring sound is preferably configured as a sinusoid.

Furthermore, the most interesting auditory evoked responses for thisapplication is, as already implied, the auditory steady state responses,which is why the response signal recorded from the electrodes preferablyis the auditory steady state responses (ASSR).

The embodiments of the disclosure may be best understood from thefollowing detailed description taken in conjunction with theaccompanying figures. The figures are schematic and simplified forclarity, and they just show details to improve the understanding of theclaims, while other details are left out. Throughout, the same referencenumerals are used for identical or corresponding parts. The individualfeatures of each embodiment may each be combined with any or allfeatures of the other embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments, features and/or technical effect will be apparent fromand elucidated with reference to the illustrations described hereinafterin which:

FIG. 1 illustrates various parts of the system according to anembodiment of the disclosure;

FIG. 2 illustrates parts of the system according to an embodiment of thedisclosure;

FIG. 3 illustrates various parts of the system according to FIG. 1 ,wherein the naturally occurring sound is recorded as speech from e.g. amother to a child;

FIG. 4 illustrates various parts of the system according to FIG. 2 ,wherein the naturally occurring sound is recorded as a speech from e.g.a mother to a child;

FIG. 5 illustrates an example of a speech signal in the time domain;

FIG. 6 illustrates a frequency spectrum of the speech signal of FIG. 5 ;

FIG. 7 illustrates a modulation function and the signal resulting fromapplying said modulation function to the speech signal of FIG. 5 ;

FIG. 8 illustrates a frequency spectrum of the modulated signal in FIG.7 ;

FIG. 9 illustrates schematically a preferred embodiment of the method ofgenerating the ASSR speech stimulus;

FIG. 10 illustrates example modulation powers of bandpass filteredversions of an international standardized speech signal;

FIG. 11 illustrates example modulation powers of bandpass filteredversions of a four-band modulated international standardized speechsignal;

FIG. 12 illustrates the long-term one-octave power spectra of aninternational standardized speech signal, as well as a four-bandmodulated international standardized speech signal, after adjusting theamplitude of each of the four component bands.

DETAILED DESCRIPTION

Referring initially to FIG. 1 , an illustration of various parts of thesystem according to an embodiment of the disclosure is shown. As seen inFIG. 1 , the system 1 comprises a diagnostic device 2, one or moreelectrodes 31, 32 and a sound emitting device 4. Furthermore, FIG. 1illustrates the setup of the system 1 in a diagnostic validation mode,where a child 3 is presented with a sound stimulus via the soundemitting device 4, and has arranged on the scalp 33 the one or moreelectrodes 31, 32, so that the system may perform a hearing test,especially a validation test to evaluate the performance of a hearingaid ability to compensate for the hearing impairment of the child.

As illustrated, the one or more electrodes 31, 32 are configured to bearranged on the scalp 33 of the child 3 (or other hearing impaired testperson) under test and are configured to be connected to the diagnosticdevice 2 (e.g. via wires 42 or alternatively in a wireless manner). Inthe embodiment shown in FIG. 1 , the sound emitting device 4 isconfigured as a probe which is connected to the diagnostic device 2 andis configured to transmit a sound stimulus 41 into the ear of the child3. The sound stimulus 41 may as will be apparent in the followingdescription of the embodiments be generated in the diagnostic device 2or externally thereto.

The diagnostic tool 2 is in more detail configured to be set in at leasta validation mode. Thus, the diagnostic tool 2 may comprise a controlunit 24 configured to control one or more modes of operation, but forthis application the validation mode is considered in more detail inlight of validating the performance of the hearing aid after havingfitted the hearing aid to e.g. a child. Furthermore, the diagnostic toolcomprises a signal generator (SG) 22, which is configured to transmitthe generated stimulus to the sound emitting device 4. For recording theobtained responses from the electrodes 31, 32 arranged on the scalp 33of the child 3, the diagnostic device is configured with a recordingprocessor (RP) 23, which takes as input the responses obtained by theelectrodes 31, 32. Accordingly, the diagnostic tool 2 is configured tobe controlled by a user, e.g. a hearing care professional, a doctor orother professional who has the intention of testing, screening, and mostrelevant for this application to validate a hearing aid fitting to e.g.a hearing impaired small child. As will become apparent the diagnostictool is when controlled into a validation mode configured to cause thesignal generator 22 to generate a sound stimulus and to transmit thegenerated sound stimulus to the sound emitting device 4, wherein thegenerated sound stimulus is configured as an amplitude and/or frequencymodulated naturally occurring sound.

Several notes should be mentioned here. First, it should be noted thatthe sound stimulus may be generated in the diagnostic tool, but may alsobe generated externally thereto. Secondly, the sound emitting device maybe a probe as illustrated schematically in FIG. 1 , but could similarlybe a loudspeaker as illustrated in FIG. 2 . In addition, it should benoted that the sound emitted to the ear should preferably undergo aprocessing scheme corresponding to the processing performed by a hearingaid before the sound is presented to the ear. Thus in a preferred inembodiment, the child under test should have hearing aids arranged onthe ears, and sound should be emitted to the ear via the hearings aids.When sound is presented via a loudspeaker, one ear is tested at a time,and the non-tested ear should be plugged, e.g. with a foam ear-plug.

In general, with a system as described herein, the hearing aidperformance can be evaluated for a child having a hearing impairment andwho is unable to provide a response to a signal transmitted to the earof the child. Thus, this objective validation setup provided by thesystem allows a stimulus which when processed by the hearing aid is notconsidered as noise and does activate the brain of the child in suchmanner that the electrodes can record the auditory steady stateresponses, which the stimulus evoke. It should be noted that currentvalidation methods merely rely on the face changes, noises or similarspontaneous physical changes that the child expresses when beingpresented with different stimuli, while this system and method allows anobjective evaluation of the performance of the hearing aid, rather thanthe subjective evaluation based on e.g. facial expressions from thechild under test.

In the following, different system setups will be explained in moredetail and finally the method of generating the sound stimulus which maybe based on a naturally occurring sound, preferably speech, will bedescribed. It should be noted that corresponding features for eachembodiment will have the same number adhered thereto in the followingdescription of various embodiments.

Referring now to FIG. 2 , a preferred setup for the system is described.Here the setup is more or less as described in relation to theembodiment of FIG. 1 , wherein the differences lies in that the soundemitting device is configured as a loudspeaker 25, which is connectedeither wired or wirelessly 26 to the diagnostic tool 2 and emits thegenerated sound stimulus 41. In this embodiment, the child 3 is wearingthe hearing aid (or hearing aids) 104, of which the performance shouldbe evaluated. In the setup according to FIG. 2 , it is preferred thatonly one ear is tested at a time, while the second ear is plugged, asalready explained above. Accordingly, in this setup, the diagnostic tool2 is set in the validation mode 21 via the control unit 24 andconfigured to generate a sound stimulus, which is configured as anamplitude and/or frequency modulated naturally occurring signal. Thegenerated stimulus is transmitted wirelessly or wired to the loudspeaker25, which emits the sound stimulus 41. The emitted sound stimulus ispicked up by the hearing aid 104, which processes the sound stimulus ina regular manner in accordance with the hearing aid settings, and thenemits the sound stimulus into the ear 34 of the child 3.

The emitted sound stimulus evokes a brain response known as the auditorysteady state response (ASSR), which is picked up by the electrodes 31,32 arranged on the scalp 33 of the child 3. The ASSR signals picked upby the electrodes 31, 32 is transmitted to the diagnostic device 2wherein a detection scheme is used to detect if a response is present ornot. The important note here, and for all of the other embodimentsdescribed, is that the sound stimulus is processed by the hearing aid ina similar manner as normal speech, while at the same time being able toevoke the ASSR.

In another embodiment illustrated in FIG. 3 , most of the featuresdescribed in the previous embodiments are present and the respectivenumbers adheres thereto. In FIG. 3 an embodiment, wherein the soundstimulus is generated from a recording of a naturally occurring sound isillustrated. Here the naturally occurring sound is configured as aspeech signal 7 which is recorded via a recording device 5. The recordedspeech signal 7 is input to the diagnostic device 2 via e.g. atransmission line 51, such as a wired or wireless transmission. In thediagnostic device 2, the recorded speech signal 7 is input to the soundstimulus generator 22, wherein the sound stimulus generator 22 generatesan amplitude and/or frequency modulation of the speech. This creates thesound stimulus 41 which is delivered to the child 3 via a probe asillustrated in FIG. 3 or preferably via a loudspeaker 25 and a hearingaid 104, as illustrated in the embodiment of FIG. 4 . By providing asystem setup, where e.g. a parent's voice, such as the voice of themother, can be recorded, processed, and used as frequency and/oramplitude modulated stimulus signal, it is ensured that the child 3 fromearly stages on hears a known voice and at the same time the parentswill actually experience that their child is able to hear their voices.

As implied, the embodiment of FIG. 4 illustrates a similar setup asdescribed in relation to FIG. 3 . However, in the embodiment of FIG. 4 ,the sound stimulus 41 is presented to the hearing aid 104 via aloudspeaker, as also described in relation to FIG. 2 . Thus in thissystem setup, the parent 6 (illustrated as a mother) provides a speechsignal 7 which is recorded by a microphone 5. The signal is transmitted51, either wired or wirelessly to the diagnostic device 2, wherein inthe diagnostic device a sound stimulus generator 22 generates the soundstimulus 41 used to evoke the brain responses, such as the auditorysteady state responses. The remaining processes are similar to what hasbeen described in the previous embodiments, and will therefore not beelaborated on in further detail. As also described in relation to theembodiment of FIG. 2 , it is in this setup preferred that only one earis tested at a time, while the second ear is plugged.

It should be noted that for each of the system setups described in theabove embodiments, the diagnostic device is illustrated schematically asa computer. However, this should not be limiting to the understandingthat the diagnostic device could similarly be constituted by a dedicatedhand-held or table-top diagnostic device, which has the same featuresincorporated therein.

In addition, the naturally occurring sound used for generating the soundstimulus evoking ASSR signals, could be a standardized speech signal,which is stored in a memory in the diagnostic device 2.

In another note, in case of e.g. a recorded speech signal, as describedin relation to FIGS. 2 and 4 , it should be noted that this recordedspeech signal could be processed in an auxiliary device to thediagnostic tool, and then input to a memory or the signal generator ofthe diagnostic device after having undergone the needed processing (tobe explained in the following) to be able to create a naturallyoccurring speech signal, which has features enabling the speech stimulusto evoke ASSR signals in the brain without being classified as noise bya hearing aid.

Until now the system set up in a diagnostic validation mode of thesystem has been explained in detail. In the following, the actualprocessing of the naturally occurring sound needed to generate anaturally occurring sound, preferably speech, which can be used as anASSR evoking stimulus, will be explained in detail.

Referring initially to FIGS. 5 and 6 , a time series of a naturallyoccurring sound, such as speech 7, is illustrated together with thefrequency spectrum 71 thereof. Such speech signals are preferably usedin the system described herein, since speech is most relevant forhearing. Accordingly, the speech signal illustrated in FIG. 5 could e.g.be a recorded speech signal as illustrated in FIGS. 2 and 4 .Alternatively it could be a standardized speech signal, which e.g. isstored in the diagnostic device.

In FIG. 7 it is illustrated how an amplitude modulation of the speechsignal may take place. That is, an ASSR-evoking stimulus may begenerated from a speech signal g(t) by multiplying the speech signalg(t) with a sinusoidal amplitude modulation 72 to create a stimulus asgiven in equation 1

s(t)=[1+cos(2πf _(R) t)]·g(t),  (1)

where f_(R) is the ‘repetition rate’ or modulation frequency, e.g. 90Hz. In the frequency domain this corresponds to equation 2, and theillustration shown in FIG. 8 ,

S(f)=G(f)+½[G(f−f _(R))+G(f+f _(R))],  (2)

where S and G are the spectra of s and g, respectively, and f isfrequency. In this example, the speech signal 73 is amplitude modulatedover the entire frequency range of the speech signal.

However, in a preferred embodiment, the speech signal (i.e. thenaturally occurring sound) is received in the sound signal generator(either from a recording of the speech or e.g. from a memory as previousdescribed). Generally speaking, for all of the described embodiments, itshould be understood that the speech signal (i.e. the naturallyoccurring signal) is modified as illustrated in FIG. 9 , to become anASSR stimulus. The amplitude and/or frequency modulation of the naturaloccurring sound may be performed in two alternative ways.

In a preferred first alternative, illustrated in FIG. 9 , the soundstimulus 41 is generated in the sound signal generator in the followingsteps:

First the recorded naturally occurring sound (such as speech 7) isfrequency or amplitude modulated 220 with a plurality of modulatorfunctions 221, 222, 223, 224 having different modulation rates;

Secondly each of the plurality of amplitude and/or frequency modulatedrecorded naturally occurring sounds 221, 222, 223, 224 is filtered byone of a plurality of band-pass filters 225, 226, 227, 228 chosen foreach of the modulations 221, 222, 223, 224 of the recorded naturallyoccurring sound; wherein further the amplitude and/or frequencymodulated sub-bands are combined 229 to form said sound stimulus 41.

In more detail, in relation to the system setup, the recorded speechsignal 7 is input to the signal generator 22 (refer to other embodimentsdescribed). In the signal generator, the speech signal 7 is amplitude orfrequency modulated 220 with e.g. 4 modulator functions 221, 222, 223,224, having different modulation rates. This ensures that the recordedauditory evoked responses respective to the different stimulationsub-bands (to be described) can be separated in the frequency domain.When the speech signal 7 has been modulated by e.g. 4 modulatorfunctions 221, 222, 223, 224 as illustrated in FIG. 9 , each of the 4modulated speech signals are input to a filtering process 230. In thisfiltering process, a specific band-pass filter 225, 226, 227, 228 ischosen for each of the individual modulated speech signals 221, 222,223, 224. This ensures that 4 sub-bands of the modulated speech signalis generated for the purpose of testing hearing ability in correspondingspecific frequency ranges. The sub-bands are subsequently summed 229(i.e. combined) to create the speech ASSR stimulus used for detectingASSRs in the described setup. As described previously, the thus createdspeech ASSR stimulus is transmitted to the ear, preferably via a hearingaid, by a speaker, such as a loudspeaker, ad described in relation toFIGS. 2 and 4 .

In a second alternative manner (not illustrated in more detail), thenaturally occurring sound (i.e. speech) is in the sound signal generatorprocessed in the following steps:

First the speech signal is filtered into a plurality of frequencysub-bands by means of a plurality of corresponding bandpass filters.

Secondly, the plurality of frequency sub-bands are amplitude and/orfrequency modulated. That is, each of the sub-bands are amplitude and/orfrequency modulated. This creates different frequency or amplitudemodulated sub-bands of the speech signal, which in a final step arecombined to form the sound stimulus.

For the preferred first alternative the frequency-specific embodiment ofthe invention can be devised by

${s(t)} = {\sum\limits_{i = 1}^{I}{h_{BPi}*\left\lbrack {\left( {1 + {A_{i}\cos\left( {2\pi f_{Ri}t} \right)}} \right){g(t)}} \right\rbrack}}$

where g(t) is the naturally occurring signal, preferably speech,h_(BPi)(t) are impulse responses of I band-pass filters, * denotesconvolution, f_(Ri) are the I different modulation frequencies, andA_(i) are the I modulation depths.

For the second alternative, a frequency-specific embodiment of theinvention can be devised by separating the speech signal into Isub-bands g(t)=h_(BPi)(t)*g(t) and imposing amplitude modulationsindependently at different repetition rates for each sub-band, e.g.

${s(t)} = {\sum\limits_{i = 1}^{I}{\left( {1 + {A_{i}\cos\left( {2\pi f_{Ri}t} \right)}} \right){g_{i}(t)}}}$

It should be noted that different modulation patterns may be created byadding more sidebands to the frequency modulated speech signal S(f) inthe frequency domain, or by using different modulator functions in thetime domain, e.g. [1+A·cos(2πf_(R)t)]^(N), where 0<A≤1 and N>0, tocreate a more shallow or more peaky modulation pattern.

In order to ensure that the generated sound stimulus is sufficientlyclose to the original speech signal after having been processed with thefrequency and/or amplitude modulations of the frequency sub-bands theamplitude and/or frequency modulated stimulus is adjusted in magnitudeto align with a set of predetermined values. This is preferably done byadjusting the level of each bandpass filtered component of the combinedstimulus, as shown below for the two aforementioned alternatives,respectively.

${s(t)} = {\sum\limits_{i = 1}^{I}{B_{i}h_{BPi}*\left\lbrack {\left( {1 + {A_{i}\cos\left( {2\pi f_{Ri}t} \right)}} \right){g(t)}} \right\rbrack}}$${s(t)} = {\sum\limits_{i = 1}^{I}{{B_{i}\left( {1 + {A_{i}\cos\left( {2\pi f_{Ri}t} \right)}} \right)}{g_{i}(t)}}}$

Here, the values B_(i), i=1, . . . , I are the aforementioned set ofpredetermined values. As an example, FIG. 12 shows the long-termone-octave power spectra of an international standardized speech signal,as well as a four-band modulated international standardized speechsignal, after adjusting the amplitude B_(i), i=1, . . . , 4 of each ofthe four component bands to obtain a match between the two one-octaveband spectra.

Similarly, but not illustrated, a modulated modified naturally occurringspeech signal may be adjusted in band-power so as to ensure that thespeech content corresponds to the actual unmodified recorded speechsignal.

The advantage of the amplitude-modulated speech signal (such as the ISTSsignal) over previously known signals is that it maintains importantcharacteristics of speech, which are crucial for a hearing aid'sclassification algorithms. One of the most important characteristics ofspeech used for signal classification in a hearing aid is the modulationpower. The modulation power spectrum is determined by estimating theenvelope of a signal and taking the Fourier transform of the envelope.As an exemplification of how the disclosed method preserves themodulation power structure of a speech signal, the illustrations inFIGS. 13 and 14 are provided. FIGS. 13 and 14 displays the modulationspectra computed in ⅓-octave wide frequency bands, for both the originalISTS and a four-band modulated ISTS. For the latter, the ISTS wasfiltered into four 1-octave wide frequency bands centered at 500 Hz, 1kHz, 2 kHz, and 4 kHz, each of which were 100% amplitude modulated at90.82 Hz, 97.66 Hz, 88.87 Hz, and 92.77 Hz, respectively. The results inFIGS. 13 and 14 show only minute changes to the modulation spectrabetween the original ISTS and the four-band modulated ISTS. The soundquality of the original speech (or any other carrier signal) is affectedby the amplitude modulation, but the stimulus is easily recognized.

In a further step of the stimulus generation, it should be noted thatone or more sub-bands could be left unmodified whereby a more naturalsound quality of the speech signal is maintained. Thus in a processingstep an amplitude and/or frequency modulation factor for one or more ofsaid plurality of sub-bands is set to 0, so as to leave said respectivesub-band unmodified.

It should be noted, that upon detecting a response, the specificfrequency sub-band for which a response is detected is in an embodimentset to 0 (i.e. turned off), so as to remove the specific frequency bandfor which the response is detected form the stimulus. This allow astronger contribution from the un-detected frequency sub-bands in thesound stimulus, and potentially a faster detection rate for theremaining plurality of frequency sub-bands. Thus, the stimulus ispresented to the ears of a child until all the necessary responses hasbeen detected to evaluate the entire hearing range.

In summary, it should now be clear that the inventors have come up witha way of validating the performance of hearing aids in an objectivemanner, by using a e.g. a naturally occurring and/or recorded speechsignal, which has been modulated in order to create an ASSR evokingspeech stimulus which is not considered as noise by a hearing aid.

As used, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well (i.e. to have the meaning “at least one”),unless expressly stated otherwise. It will be further understood thatthe terms “includes,” “comprises,” “including,” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element but an intervening element mayalso be present, unless expressly stated otherwise. Furthermore,“connected” or “coupled” as used herein may include wirelessly connectedor coupled. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. The steps ofany disclosed method is not limited to the exact order stated herein,unless expressly stated otherwise.

It should be appreciated that reference throughout this specification to“one embodiment” or “an embodiment” or “an aspect” or features includedas “may” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the disclosure. Furthermore, the particular features,structures or characteristics may be combined as suitable in one or moreembodiments of the disclosure. The previous description is provided toenable any person skilled in the art to practice the various aspectsdescribed herein. Various modifications to these aspects will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other aspects.

The claims are not intended to be limited to the aspects shown herein,but is to be accorded the full scope consistent with the language of theclaims, wherein reference to an element in the singular is not intendedto mean “one and only one” unless specifically so stated, but rather“one or more.” Unless specifically stated otherwise, the term “some”refers to one or more.

Accordingly, the scope should be judged in terms of the claims thatfollow.

1. A system configured to perform at least a validation mode of ahearing test, said system comprising: a diagnostic device; one or moreelectrodes configured to be arranged on the scalp of a person andconfigured to be connected to said diagnostic device; and a soundemitting device configured to be connected to said diagnostic device andto transmit a generated sound stimulus into the ear of a person, whereinthe diagnostic device includes a recording processor configured toreceive a response signal from said one or more electrodes arranged onthe scalp of a person; a control unit configured to control the mode ofoperation of said diagnostic device; and a signal generator configuredto transmit said generated stimulus to said sound emitting device, andwherein, in a validation mode of operation said signal generator isconfigured to generate said sound stimulus and to transmit saidgenerated sound stimulus to said sound emitting device, wherein saidgenerated sound stimulus is speech of a human, which is amplitude and/orfrequency modulated by the signal generator.
 2. The system according toclaim 1, wherein said sound emitting device is configured as a hearingaid or a plurality of hearing aids configured to be arranged on or inthe ear or ears of said person in said validation mode of operation. 3.The system according to claim 1 further comprising: a hearing aid or aplurality of hearing aids configured to be arranged on or in the ear orears of said person, wherein said sound emitting device is configured asan external loudspeaker, which is connected to the diagnostic device andis arranged in the ambient surroundings to the one or more hearing aids,wherein the loudspeaker is configured to receive said generated stimulusfrom said signal generator and to play said generated sound stimulus tosaid one or more hearing aids.
 4. The system according to claim 2,wherein in said validation mode, said diagnostic device is configured totransmit said generated sound stimulus to said one or more hearing aidsvia said hearing aids and/or via said external loudspeaker, whereby saidhearing aids presents said transmitted generated sound stimulus in theear of the person; and wherein said diagnostic device is configured torecord said response from said one or more electrodes arranged on saidscalp of the person, and wherein said response is provided as auditoryevoked responses (AER).
 5. The system according to claim 1, wherein saiddiagnostic device is configured to record and/or receive a recording ofsaid speech of a human, and said recorded speech of a human is recordedvia the diagnostic device and/or is transmitted wired or wirelessly tosaid diagnostic device from an auxiliary device, and the sound stimulusgenerator is configured to generate from said recorded speech of ahuman, an amplitude and/or frequency modulation of said recorded speechof a human, so as to create said sound stimulus.
 6. The system accordingto claim 5, wherein said recorded speech of a human is input to saidsound signal generator, wherein said recorded speech of a human isconfigured to be processed by the diagnostic device by: filtering saidrecorded speech of a human into a plurality of frequency sub-bands; andamplitude and/or frequency modulating each of said plurality offrequency sub-bands; and wherein said amplitude and/or frequencymodulated sub-bands are combined to form said sound stimulus.
 7. Thesystem according to claim 5, wherein said recorded speech of a human isreceived in said sound signal generator, and said diagnostic device isconfigured to process said recorded speech of a human by: processingsaid recorded speech of a human by a frequency or amplitude modulationwith a plurality of modulator functions having different modulationrates; subsequently filtering each of said plurality of amplitude and/orfrequency modulated recorded speech of a human by one of a plurality offrequency sub-bands chosen for each of the modulations of the recordedspeech of a human; and combining said amplitude and/or frequencymodulated sub-bands to form said sound stimulus.
 8. The system accordingto claim 6, wherein each of said amplitude and/or frequency modulatedfrequency sub-bands are adjusted in magnitude to align with apredetermined value.
 9. The system according to claim 6, wherein saiddiagnostic device is configured to be adjusted to set an amplitudeand/or frequency modulation factor for one or more of said plurality ofsub-bands to 0, so as to leave said respective sub-band unmodified. 10.The system according to claim 6, wherein in a first transmission theentire frequency band of said sound stimulus is played to said hearingaid(s), and upon detection of a response from said electrodes within aspecified frequency sub-band, said specific frequency sub-band is turnedoff, so as to remove the specific frequency band for which a response isdetected from said stimulus.
 11. The system according to claim 6,wherein said speech of a human is band pass filtered into at least 4frequency bands having center frequencies of 500 Hz, 1 kHz, 2 kHz, and 4kHz.
 12. The system according to claim 1, wherein the response signalrecorded from said electrodes is an auditory steady state response(ASSR).
 13. The system according to claim 6, wherein each of saidsub-bands are amplitude and/or frequency modulated with modulatorfunctions having different modulation rates for each of said sub-bands.14. A method for performing a validation mode of a hearing test for aperson incapable of providing active intentional responses, said methodcomprising: arranging one or more electrodes on the scalp of the person;transmitting a generated sound stimulus into the ear of the person by asound emitting device receiving a response signal from said one or moreelectrodes arranged on the scalp of the person, by a recording processorof a diagnostic device controlling the mode of operation of saiddiagnostic device wherein, in a validation mode of operation, generatingsaid sound stimulus by a signal generator of said diagnostic device andtransmitting said generated sound stimulus to said sound emittingdevice, wherein said generated sound stimulus is speech of a human,which is amplitude and/or frequency modulated by said signal generator.15. A diagnostic device configured to perform at least a validation modeof a hearing test for a person incapable of providing active intentionalresponses, said diagnostic device comprising: a signal generatorconfigured to transmit a generated sound stimulus to a sound emittingdevice for transmitting said generated sound stimulus into the ear ofthe person, a recording processor configured to receive a responsesignal from one or more electrodes arranged on the scalp of the person;a control unit configured to control the mode of operation of saiddiagnostic device; and wherein, in a validation mode of operation saidsignal generator is configured to generate said sound stimulus and totransmit said generated sound stimulus to said sound emitting device,wherein said generated sound stimulus is speech of a human, which isamplitude and/or frequency modulated by said signal generator.